Steel pipe is the most widely used gas pipeline project. Its main advantages are: high strength, good toughness and strong bearing capacity.
Ss, impact resistance and tightness, good plasticity, easy welding and hot working, thinner wall thickness, saving metal. However, its corrosion resistance is poor, and appropriate anti-corrosion measures are needed.


There are two main types of seamless and welded steel pipes for urban gas pipelines. High strength seamless steel pipe, but generally use small diameter steel pipe below DN200 to limit production process and cost. More types of welded steel pipe can be divided into straight seam welded steel pipe and spiral welded steel pipe. Longitudinal welded pipe (hereinafter referred to as straight welded pipe) also includes LSAW pipe and ERW pipe. Spiral welded steel pipe (ssaw steel pipe) is spiral seam double submerged arc welding (HSAW) pipe.


The manufacturing process of straight seam and spiral tube is compared. The former has the following advantages:
(1) In the manufacturing process of spiral tube, it is determined that the residual stress is greater than that of straight-seam tube. As a result of the expansion process of straight-seam tube and whole body, the residual stress is close to zero, which can not be achieved by spiral tube.


(2) In spiral welding, most of the wrong edges are in the range of 1.1-1.2 mm. The standard requires that the wrong side of the wall thickness is less than 10% of the thin-walled pipe. The wrong edge is not easy to meet the standard requirements, and there is no problem with the straight seam pipe.


Compared with straight seam pipe, spiral weld has poor fluidity and serious stress concentration.


(4) The heat-affected zone of coil is larger than that of straight-seam pipe, and the heat-affected zone of pipeline is the key to quality.


_Spiral geometric accuracy, to the construction site, as a corresponding, welding brings some difficulties.